Objectives: Exposure to light-at-night (LAN) has been reported to impair blood glucose regulation. The liver modulates blood glucose through mechanisms influenced by several factors that include peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1α) and glucose-6-phosphatase (G6Pase). This study investigated the effect of intermittent exposure to green and white LAN on some hepatic glucose regulatory factors in male Wistar rats.
Methods: Animals were divided into three equal groups. Group I (control) was exposed to normal housing conditions. Groups II and III were each daily exposed to either green or white LAN for 2 h (7-9 pm) for 14 days. Body weight and blood glucose was monitored on days 0, 7, and 14. Thereafter, retro-orbital sinus blood was obtained after light thiopental anaesthesia and serum insulin was determined. Liver samples were also obtained and evaluated for glycogen, PGC-1α, and G6Pase activity. Insulin resistance was estimated using the HOMA-IR equation.
Results: Body weight and blood glucose on days 7 and 14 increased in groups II and III compared to control. Hepatic PGC-1α and G6Pase increased in group II (2.33 ± 0.31; 2.07 ± 0.22) and III (2.31 ± 0.20; 0.98 ± 0.23) compared to control (1.73 ± 0.21; 0.47 ± 0.11). Hepatic glycogen was 71.8 and 82.4% reduced in groups II and III compared to control. Insulin in group II increased (63.6%) whiles group III values reduced (27.3%) compared to control. Insulin resistance increased in group II (0.29 ± 0.09) compared to control (0.12 ± 0.03) and group III (0.11 ± 0.03), respectively.
Conclusions: Exposure to 2 h green and white LAN in the early dark phase increases hepatic glycogenolysis and gluconeogenetic activities resulting in increased blood glucose. In male Wistar rats, exposure to green but not white LAN may predispose to insulin resistance.
Keywords: green light; hepatic glucose homeostasis; light-at-night; liver; white light.
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